Miscarriage occurs in an estimated 10% to 15% of all pregnancies of less than 20 weeks gestation (Stirrat, Lancet 336:673-675, 1990). Recurrent miscarriage is classically defined as the occurrence of three or more consecutive losses of clinically-recognized pregnancies prior to the 20th week of gestation, exclusive of molar and ectopic pregnancies. Prospective studies have assessed the risks of subsequent miscarriage after one miscarriage to be 15%, rising to 17% to 31% after two miscarriages, and 25% to 46% after three or more miscarriages. Although the loss of one pregnancy (or sometimes even two pregnancies) is considered by many clinicians to be within the range of normal (and likely due to gamete failure), loss of three or more pregnancies is generally considered to be associated with a pathological condition. Most providers will initiate an evaluation for recurrent pregnancy loss (RPL) after two or more consecutive miscarriages.